Hi there,
Nice itinrary! Personally I think Kyushu is always a great place to go!
Your itinarary currently consists of the following tickets:
Fukuoka --> Yufuin ¥ 4,430
Yufuin --> Buppu ¥ 1,080
Beppu --> Tokyo :¥ 23,950
Tokyo --> Kanazawa ¥ 12,710
Kanazawa --> Tokyo ¥ 12,710
For a total of ¥ 54,880.
A 7-day JR-Pass is ¥ 28,300 so if you could do your trip with that you really would make a home run savings wise (¥ 26,580), it would mean however moving your trip to Kanazawa back by a day.
The 14-Day JR-Pass is ¥ 45,100 even with this one you would make some good savings (¥ 9,780) and you would have some extra days left, so you could use the pass to return to the Airport for instance as well.
Hope this helps,
Daniel